Lubricating oil composition for internal combustion engine

ABSTRACT

A lubricating oil composition comprising a GTL (Gas to-Liquid) base oil synthesized by the Fischer-Tropsch process and a viscosity index improver, wherein the content of the viscosity index improver is 0.1 to 20 mass %, and at least HTHSV 50° C./HTHSV 150° C. is 6.50 or less and KV 50° C./HTHSV 150° C. is 8.00 or less.

FIELD OF THE INVENTION

The present invention relates to a lubricating oil composition for an internal combustion engine (hereinafter also referred to as an engine) that is excellent in fuel economy in a temperature range of practical use.

BACKGROUND OF THE INVENTION

Regulations regarding environmental conservation are being strengthened on a global scale. Limitations on fuel consumption and limitations on exhaust gases, particularly when it comes to automobiles, are becoming increasingly severe, based on concerns regarding environmental problems, such as global warming, depletion of petroleum resources, as a strategy for preserving resources. In particular when it comes to the need to reduce fuel consumption of automobiles, improvements are being made to engines in order to reduce the weight of automobiles and to improve energy efficiency, and improvements are being made to various types of structural elements in automobiles, such as improving the efficiency of transmission of the driving forces.

In engine oils there is the need to reduce frictional loss in the engine in order to contribute to reduced fuel consumption. This friction loss is primarily due to viscous drag under the conditions of fluid lubrication, caused by the lubricating oil that is used, and friction between metals in the sliding portions under mixed lubrication or boundary lubrication conditions, and thus, in order to achieve a superior effect in fuel economy, it is necessary to reduce the viscosity below that which is conventional for the viscosity of lubricating oil, to reduce the viscous drag. Preventing variability in viscosity due to changes in temperature, using a base oil with a lower viscosity, or a viscosity index improving agent, such as a comb polymer, or the like, is effective in reducing the viscosity of a lubricating oil (as described in, for example, Japanese Patent Application No. 2015-520285 and Japanese Patent No. 5502730).

In relation to this, in recent years, in particular, as a typical example of a strategy to reduce fuel consumption of passenger vehicles, there is a function to stop idling that works when a passenger vehicle comes to a halt, such as at a signal, and thus engines are stopped frequently when traveling on city streets. Because of this, when operating over short distances, such as when on a shopping trip, engine operation is stopped without the temperature of the internal combustion engine lubricating oil warming up adequately. The same is true for a plug-in hybrid vehicle (PHV), where the engine is turned ON/OFF as necessary, producing a state wherein there is a tendency for the engine to not warm up adequately with short-distance commutes or shopping trips.

On the other hand, it is known that reducing the viscosity of the engine oil leads to an increased risk of wear and metal-on-metal friction due to failure of the oil film when at high temperatures, and thus, to prevent this, the SAE J300 viscosity standard defines lower limits for the 150° C. shear viscosity (hereinafter termed “HTHSV150”) and the 100° C. kinematic viscosity (hereinafter termed “KV100”) for each viscosity grade. Because of this, when attempting to reduce the viscosity of engine oils, the lower limit values for HTHSV150 and KV100 become barriers, and no specific methods have been proposed for achieving further fuel economy at given viscosity grades, even for PHVs and for vehicles with functions for stopping idling.

In light of the above, the present invention is to achieve a lubricating oil composition for an internal combustion engine that is able to further improve fuel economy under general driving conditions, including a state wherein the engine itself is not running, while still maintaining HTHSV150 and KV100, stipulated in SAE J300, at no less than the lower limit value.

SUMMARY OF THE INVENTION

The present inventors, based on the issues set forth above, used a new approach to be the first to discover that it is possible to improve fuel economy substantially through having both the shear viscosity and kinematic viscosity at 50° C. be within a specific range (a specific range that corresponds to temperature characteristics in a higher temperature domain), particularly in an idling stopping vehicle and a PHV wherein the engine is stopped and started repeatedly, through extensive research regarding characteristics in a variety of temperature ranges that are not normally examined. The result was achievement of the present invention, which is able to improve the fuel economy of an internal combustion engine lubricating oil composition while maintaining the HTHSV 150° C. and KV 100° C. at no less than the lower limit values stipulated in SAE J300.

The present invention, specifically, provides (1) to (5) as follows:

(1): A lubricating oil composition for an internal combustion engine, comprising a GTL (Gas To Liquid) base oil synthesized by the Fischer-Tropsch method and a viscosity index improver, wherein the content of the viscosity index improver relative to the total amount of lubricating oil composition is 0.1 to 20 mass % by resin amount, and the lubricating oil composition satisfies the following (A) to (E): (A) high temperature high shear viscosity (HTHSV (ASTM D4683 or ASTM D5481)) at 150° C., 106 s-1 is 1.0 mPa·s or more; (B) kinematic viscosity (KV (JIS K2283)) at 100° C. is 3.0 mm2/s or more; (C) HTHSV50° C./HTHSV 150° C. is 6.50 or less; (D) KV50° C./HTHSV150° C. is 8.00 or less; and (E) NOACK evaporation amount (JPI-5S-41) is 15 mass % or less. (2): The lubricating oil composition of (1), including: one or more base oils having KV100° C. of 1 to 8 mm2/s, a viscosity index of 110 or more, % CA by ASTM D3238 of 5 or less, and % CP by ASTM D3238 of 60 or more, wherein: the content of the base oils relative to the total amount of the lubricating oil composition is 50 mass % or less, and a fraction of an entire base oil at 380° C. or less in gas chromatography distillation by ASTM D2887 is 10 mass % or less. (3): The lubricating oil composition of (1) or (2), wherein: at least one of (F) through (I), below, is satisfied: (F) the lubricating oil composition includes a metal-including detergent having at least one selection from Ca and Mg, and [Ca]+[Mg]=0.10 to 0.25, where [Ca], [Mg] are respectively concentrations (mass %) of calcium and magnesium in the lubricating oil composition; (G) the lubricating oil composition contains a succinimide ashless dispersant and/or a boron modified succinimide ashless dispersant, and the dispersants are 0.01 to 0.20 mass % (based on a total amount of the lubricating oil composition) in terms of nitrogen concentration; (H) the lubricating oil composition includes ZnDTP of 0.03 to 0.09 mass % (based on the total amount of the lubricating oil composition) in terms of phosphorus concentration; and (I) the lubricating oil composition includes an organic molybdenum compound of 0.01 to 0.12 mass % (based on the total amount of the lubricating oil composition) in terms of Mo concentration. (4): The lubricating oil composition of any of (1) to (3), including at least one selection from a corrosion inhibitor, a phenol-based antioxidant, an amine-based antioxidant, and a sulfur-containing additive. (5): The lubricating oil composition of any of (1) to (4), wherein the viscosity index improver is a comb polymer, preferably wherein the comb polymer comprises (1) repeating units derived from polyolefin-based macro monomers, and (2) repeating units derived from low-molecular-weight monomers selected from a group comprising styrene monomers having between 8 and 17 carbon atoms, alkyl(meth)acrylates having between 1 and 10 carbon atoms in an alcohol base, vinyl esters having between 1 and 11 carbon atoms in an acyl, vinyl ethers having between 1 and 10 carbon atoms in an alcohol base, (di)alkyl fumarate having between 1 and 10 carbon atoms in an alcohol base, (di)alkyl maleates having between 1 and 10 carbon atoms in an alcohol base, and mixtures of these monomers, included in the main chain.

The compositions of the present invention are particularly well-suited for PHVs and/or stop-idle vehicles.

The present invention provides an internal combustion engine lubricating oil composition able to improve fuel economy while maintaining the HTHSV 150 and KV 100 at no less than the lower limit values stipulated in SAE J300.

In the present invention, an internal combustion engine lubricating oil composition satisfies the 150° C. 106 s-1 high-temperature/high-shear viscosity {(ASTM D4683 or ASTM D5481), hereinafter termed “HTHSV”} is no less than 1.0 MPA-s, and the 100° C. kinematic velocity {(JIS K2283), hereinafter termed “KV”) is no less that 3.0 mm2/s, and the NOACK evaporation (JPI-5S-41) is no less that 15 mass %, and HDHSV 50° C./HTHSV 150° C.≤6.50 and KV 50° C./HTHSV 150° C.≤8.00.

The composition, methods for manufacturing, characteristics, and applications of the internal combustion engine lubricating oil composition according to the present invention will be explained in detail below, but the present invention is in no way limited thereto.

DETAILED DESCRIPTION

The internal combustion engine lubricating oil composition according to the present invention includes a base oil and a viscosity index improving agent, and, if necessary, includes other additives as well. The composition according to the present invention will be explained below.

The base oil in the lubricating oil composition according to the present invention includes, as an essential component, a GTL (gas-to-liquid) base oil, synthesized using the Fischer-Tropsch method. The GTL (gas-to-liquid) base oil that is synthesized using the Fischer-Tropsch method, which is a technology for turning natural gas into a liquid fuel, when compared to a mineral oil base oil that is refined from crude oil, is extremely low in sulfur content and aromatic components, and extremely high in its proportion of paraffin structures, and thus the evaporative loss will also be extremely low and the oxidation stability will be superior, making this suitable as a base oil for the present invention. While there is no particular limitation on the viscosity characteristic of the GTL base oil, normally the kinematic viscosity at 100° C. may be between 1.0 and 50.0 mm²/s, more preferably between 1.0 and 12.0 mm²/s, and, more preferably, between 3.0 and 10.0 mm²/s. Moreover, normally the viscosity index may be between 100 and 180, and preferably between 105 and 160, and more preferably be between 110 and 150.

Moreover, normally the total sulfur content may be less than 10 ppm, and the total nitrogen content may be less than 1 ppm. The GTL base oil product may be Shell XHVI (registered trademark).

Note that the lubricating oil composition according to the present invention may include other base oils if necessary. Mineral oils and hydrocarbon-based synthetic oils, known as highly refined base oils, may be used as the other base oils, and, in particular, a base oil selected from a group comprising base oils classified in group 2, group 3, and group 4 of the API (American Petroleum Institute) Base Oil Classifications may be used. The base oil used here has a 100° C. kinematic viscosity of between 3.0 and 12.0 mm²/s, but preferably may be between 3.0 and 10.0 mm²/s, and more preferably between 3.0 and 8.0 mm²/s. The viscosity index of the base oil may be between 100 and 180, and preferably between 100 and 160, and more preferably between 100 and 150. The sulfur element content of the base oil may be no greater than 300 ppm, and preferably no greater than 200 ppm, more preferably no greater than 100 ppm, and even more preferably no greater that 50 ppm. Moreover, the density of the base oil at 15° C. may be between 0.80 and 0.95 g/cm³, preferably between 0.80 and 0.90 g/cm³, and more preferably between 0.80 and 0.85 g/cm³.

The group 2 base oil may be a paraffin-based mineral oil obtained through, for example, the use of an appropriate combination of refining means, such as hydrocracking, dewaxing, and the like, to a lubricating oil fraction obtained through low-pressure distillation of crude oil. Moreover, a group 2 base oil refined through the hydrorefining of Gulf Corporation, or the like, has a total sulfur content of less than 10 ppm, and an aromatic content % CA of no greater than 5 ppm, and is suitable for use as a base oil that is mixed into the lubricating oil composition according to the present invention. In the group 2 base oil, preferably the viscosity index (where the viscosity index in the present invention is measured using ASTM D2270 or JIS K2283) is no less than 100 and is less than 120, and more preferably is no less that 105 and less than 120. The 100° C. kinematic viscosity of the group 2 base oil (where the kinematic viscosity in the present invention is measured using ASTM D445 or JIS K 2283) preferably is between 3.0 and 12.0 mm²/s, and more preferably between 3.0 and 9.0 mm²/s. Moreover, in the group 2 base oil, preferably the total sulfur content is less than 300 ppm, more preferably less than 200 ppm, even more preferably less than 100 ppm, and particularly preferably less that 10 ppm. The total sulfur content is a value that is measured using a radioexcitation method (based on ASTM D4294 and JIS K2541-4). The total nitrogen content of the group 2 base oil may be less than 10 ppm, and preferably less than 1 ppm. Moreover, the aniline point of the group 2 base oil (where the aniline point in the present invention is measured through ASTM D611 and JIS K2256) preferably is between 80 and 150° C., and more preferably between 100 and 135° C.

The group 3 base oil may be, for example, a “paraffin-based mineral oil obtained through the application of high-level hydrorefining means to a lubricating oil fraction obtained through low-pressure distillation of crude oil,” “a base oil refined through the Mobil wax (WAX) isomerizing process,” or the like.

The group 3 base oil viscosity index preferably is between 120 and 150, and more preferably is between 120 and 140. The group 3 base oil 100° C. kinematic viscosity preferably is between 3.0 and 12.0 mm²/s, and more preferably between 3.0 and 9.0 mm/s. Moreover, the group 3 base oil total sulfur content preferably is less than 100 ppm, and more preferably is less than 10 ppm. The group 3 base oil total nitrogen content preferably is less than 10 ppm, and more preferably less than 1 ppm.

Moreover, the group 3 base oil aniline point is preferably between 80 and 150° C., and more preferably between 110 and 140° C.

The group 4 base oil may be, for example, a polyalphaolyfin, an alphaolefin oligomer, a mixture thereof (a polyalphaolyfin and an alphaolefin oligomer), or the like. The polyalphaolyfin (PAO) is any of a variety of polymers of alphaolefins (monomers). Moreover, the polyalphaolyfin may be a mixture wherein a plurality of types of copolymers of “alphaolefins (monomers)” are mixed, rather than a single type of “polymer of alphaolefins (monomers).” Moreover, the alphaolefin oligomer is any of a variety of types of oligomers of alphaolefins (monomers), and includes hydrogenated oligomers of alphaolefins (monomers). There is no particular limitation on the alphaolefins (monomers), and they may be, for example, ethylene, propylene, butene, an alphaolefin with a carbon number of five or more, or the like.

The hydrocarbon-based synthetic oil may be, for example, a polyolefin, including a PAO, or the like, described above, alkyl benzene, alkyl naphthalene, or the like, or a mixture, or the like, thereof.

There are no particular limitations on the viscosities of these synthetic base oils, but the 100° C. kinematic viscosity is preferably between 3.0 and 12.0 mm²/s, more preferably between 3.0 and 10.0 mm²/s, and even more preferably between 3.0 and 8.0 mm²/s. The viscosity index of the synthetic base oil, for the case of alkyl benzene or alkyl naphthalene, preferably is between 10 and 120, more preferably between 20 and 120, and even more preferably between 20 and 110, and, in the case of a polyalphaolefin, preferably is between 100 and 170, more preferably between 110 and 170, and even more preferably between 110 and 155. The 15° C. density of the synthetic base oil is preferably between 0.8000 and 0.9500 g/cm³, more preferably between 0.8100 and 0.9500 g/cm³, and even more preferably between 0.8100 and 0.9200 g/cm³.

Moreover, the base oil of the present lubricating oil composition may have a base oil belonging to group 1 of the Base Oil Categories of the API (American Petroleum Institute), mixed into the base oil described above. The group 1 base oil may be a paraffin-based mineral oil obtained through, for example, the use of an appropriate combination of refining means, such as solvent refining, hydrorefining, dewaxing, and the like, to a lubricating oil fraction that is obtained through atmospheric-pressure distillation of crude oil. In the group 1 base oil used here, the 100° C. kinematic viscosity may be between 3.0 and 35.0 mm²/s, but preferably may be between 3.0 and 10.0 mm²/s, and more preferably between 3.0 and 8.0 mm²/s. Moreover, the viscosity index may be between 90 and 120, and preferably between 95 and 115, and more preferably be between 95 and 110. Moreover, the sulfur content may be between 0.03 and 0.7 mass %, and preferably between 0.1 and 0.7 mass %, and more preferably between 0.4 and 0.7 mass %. Moreover, the % CA, in ASTM D3238, may be 5 or less, or preferably no greater than 4, or more preferably no greater than 3.4. Moreover, the % CP, in ASTM D3238, may be 60 or more, or preferably no less than 63, or more preferably no less than 66.

Moreover, in the lubricating oil composition according to the present invention, one or more base oils wherein the KV 100° C. is between 1 and 8 mm²/s, the viscosity index is no less than 110, and the % CA is no greater than 5 and the % CP is no less than 60, according to ASTM D3238, may be included, so as to be no more than 50 mass % of the lubricating oil composition as a whole, so that the fracture at 380° C. or less in gas chromatographic distillation through ASTM D2887, in the base oil as a whole, is no more than 10 mass %. The use of such a base oil makes it possible to provide a lubricating oil composition wherein a portion of the GTL oil is replaced with another base oil without a significant loss in the reduction of evaporative loss, which is a distinctive feature of the GTL oil.

Viscosity index improving agents generally are polymer substrates that have the effect of improving the viscosity index. A variety of viscosity index improving agents may be used in the present invention. Examples of viscosity index improving agents include poly(meth)acrylate and olefin copolymers such as ethylene/propylene copolymers and styrene/diene copolymers, and the like, as non-dispersive viscosity index improving agents, along with dispersive viscosity index improving agents such as those that can be obtained through copolymerization of these with monomers that include nitrogen. A comb polymer, which has a high viscosity index improving effect and is useful in reduction of (design of) the low-temperature viscosity, is preferred as a viscosity index improving agent. Note that the comb polymer is a polymer that forms a comb shape through combining, with polymer main chains, relatively long side chains that are known polymers. A known comb polymer may be used as such a comb polymer. More specifically, a comb polymer may be used wherein (1) repeating units derived from polyolefin-based macro monomers and (2) repeating units derived from low-molecular-weight monomers selected from a group comprising styrene monomers having between 8 and 17 carbon atoms, alkyl(meth)acrylates having between 1 and 10 carbon atoms in an alcohol base, vinyl esters having between 1 and 11 carbon atoms in an acyl, vinyl ethers having between 1 and 10 carbon atoms in an alcohol base, (di)alkyl fumarate having between 1 and 10 carbon atoms in an alcohol base, (di)alkyl maleates having between 1 and 10 carbon atoms in an alcohol base, and mixtures of these monomers, are included in the main chain. In particular, that which is suitable has a molar branching level of between 0.3 and 1.1 mol %, wherein, in relation to the mass of the repeating units, described above, the total of the (1) repeating units derived from polyolefin-based macro monomers and (2) repeating units derived from low-molecular-weight monomers selected from a group comprising styrene monomers having between 8 and 17 carbon atoms, alkyl(meth)acrylates having between 1 and 10 carbon atoms in an alcohol base, vinyl esters having between 1 and 11 carbon atoms in an acyl, vinyl ethers having between 1 and 10 carbon atoms in an alcohol base, (di)alkyl fumarate having between 1 and 10 carbon atoms in an alcohol base, (di)alkyl maleates having between 1 and 10 carbon atoms in an alcohol base, and mixtures of these monomers, is no less than 80 mass %, with the repeating units derived from the polyolefin-based macro molecule being between 8 and 30 mass %, and wherein the iodine number is no greater than 0.2 g per 1 g of the comb polymer.

Here the inclusion proportion of the viscosity index improving agent is between 0.1 and 15 mass %, in terms of the amount of resin, relative to the lubricating oil composition as a whole, and, more preferably, is between 0.1 and 10 mass %, in terms of the amount of resin.

In the lubricating oil composition according to the present invention, additives other than the viscosity index improving agent (other additives) may include Ca/Mg-based cleaning agents (metal-including cleaning agents that include at least one selection from Ca and Mg), succinimide-based/boron-modified succinimide-based ashless dispersing agents, ZnDTP, and/or friction adjusting agents (which may be organic molybdenum compounds). Moreover, corrosion inhibitors, phenol-based oxidation inhibitors, amine-based oxidation inhibitors, and/or sulfur-including additives may be used suitably as other additives. Other additives such as these will be explained below.

In the lubricating oil composition according to the present invention, a Ca-based cleaning agent (a cleaning agent that includes at least Ca) and/or a Mg-based cleaning agent (a cleaning agent that includes at least Mg) may be included, where the inclusion proportion thereof is suitably in a range that satisfies [Ca]+[Mg]=0.10 to 0.25 (wherein [Ca] and [Mg] are the respective concentrations (mass %) of calcium and magnesium in the lubricating oil composition). Note that if [Ca]+[Mg] is between 0.10 and 0.25, [Mg] may be 0 (that is, no Mg is included) or [Mg] may be greater than zero (that is, some or all of the Ca-based cleaning agent is replaced with a Mg-based cleaning agent). When [Ca]+[Mg] does not exceed 0.25, there is the benefit of achieving an improvement in the torque improvement ratio, and when not less than 0.10, cleanliness will be improved.

The Ca/Mg cleaning agent may be a known metal-including cleaning agent, including calcium and/or magnesium as an alkaline earth metal. Note that such a metal-including cleaning agent may include a phenate, a salicylate, a carboxylate, or a sulfonate as the main component thereof.

The lubricating oil composition according to the present invention may include a succinimide-based ashless dispersing agent and/or a boron-modified succinimide-based ashless dispersing agent, and the inclusion proportion thereof may satisfy a condition between 0.01 and 0.20 mass % (in reference to the total amount of the lubricating oil composition), in terms of the nitrogen concentration. Note that being no greater than 0.20 mass %, in terms of the nitrogen concentration, is useful in wear resistance.

That which is known may be used for a bis-type succinimide-based ashless dispersing agent that does not include boron, and a bis-type succinimide wherein, at the time of imidization, anhydrous succinic acid is added to both ends of a polyamine may be used. Moreover, that which is known to be used for the boron-modified succinimide-based ashless dispersing agent may be used, and may be a succinimide wherein a mono-type succinimide, to which, at the time of imidization, anhydrous succinic acid has been added to one end of a polyamine, and/or a bis-type succinimide wherein anhydrous succinic acid has been added to both ends of a polyamine, has been boron-modified.

The lubricating oil composition according to the present invention may include ZnDTP, and the inclusion portion thereof may be between 0.03 and 0.09 mass %, as a phosphorous inclusion proportion (in reference to the total amount of the lubricating oil composition). Note that ZnDTP has a function as an anti-wear agent, and if the phosphorus inclusion proportion is no less than 0.03 mass %, the wear resistance will be more superior. Moreover, if the phosphorus inclusion proportion is no greater than 0.09 mass %, it is unlikely to interfere with the effect of the friction adjusting agent.

ZnDTP is an abbreviation for Zinc Dialkyldithiophosphate, and is expressed by structural formula (1), below. In the equation, R indicates mutually independent hydrocarbon groups. Preferably they are primary or secondary alkyl groups of between C3 and C20. More preferably, they are primary or secondary alkyl groups of between C3 and C10.

An arbitrary compound that is normally used as a lubricating oil friction adjusting agent may be used in the lubricating oil composition according to the present invention, and may be, for example, an organic molybdenum compound or ashless friction adjusting agent. An organic molybdenum compound and an ashless friction adjusting agent may be used either singly or in combination.

That which is known may be used for the organic molybdenum compound and may be, for example, molybdenum dithiocarbamate (which may be abbreviated simply MoDTC, or the like), a trinuclear molybdenum compound as described in WO-98/26030, a sulfide of molybdenum, a molybdenum dihiophosphate salt, a molybdenum-amine complex, a molybdenum-succinimide complex, a molybdenum salt of an organic acid, a molybdenum salt of an alcohol, or the like. The inclusion proportion thereof, in an arbitrary combination of the organic molybdenum compounds, may satisfy between 0.01 and 0.12 mass % in terms of the Mo concentration (in reference to the total amount of the lubricating oil composition). Note that the storage stability is better at no more than 0.12 mass %, in terms of the Mo concentration.

That which is known conventionally may be used as the ashless friction adjusting agent, and may be, for example, an alkyl group or alkynyl group with a carbon number between 3 and 30, and, in particular, may be an ashless friction adjusting agent, such as an amine compound, a fatty acid ester, a fatty acid amide, a fatty acid, an aliphatic alcohol, an aliphatic ether, or the like, which has, in the molecule, at least one straight-chain alkyl group or straight-chain alkynyl group with a carbon number between 3 and 30. Note that some or all of these alkyl groups or alkynyl groups may be replaced with alkoxy groups, or carbon atoms of the alkyl groups or alkynyl groups may be replaced by hetero atoms. Note that while there is no particular limitation on the inclusion proportion for the ashless friction adjusting agent, it may, for example, satisfy 0.01 to 1.0 mass % (in reference to the total amount of the lubricating oil composition). Note that the storage stability and seal compatibility will be improved if this is no greater than 1.0 mass %.

In the present invention, molybdenum dithiocarbamate is the most suitable from the perspective of optimally reducing friction.

The lubricating oil composition according to the present invention may include a corrosion inhibitor.

That which is known may be used for the corrosion inhibitor, which may be, for example, a benzotriazole-based, tolyltriazole-based, thiadiazole-based, or imidazole-based compound, or the like.

Note that while there is no particular limitation on the inclusion proportion, it may be, for example, between 0.01 and 0.1 mass % (in reference to the total amount of the lubricating oil composition).

A phenol-based oxidation inhibitor and/or an amine-based oxidation inhibitor may be included as an ashless oxidation inhibitor in the lubricating oil composition according to the present invention.

That which is known may be used as the phenol-based oxidation inhibitor, which may be, for example, 4, 4′-methylene bis (2, 6-di-tert-butyl phenol), 4, 4′-bis (2, 6-di-tert-butyl phenol), or the like. That which is known may be used for the amine-based oxidation inhibitor, which may be, for example, alkyl diphenyl amine, alkyl naphthyl amine, phenyl-alpha-naphthyl amine, alkyl phenyl-alpha-naphthyl amine, or the like, which are aromatic amine compounds.

While there is no particular limitation on the inclusion proportion for the amine-based oxidation inhibitor, it should be, for example, between 0.1 and 2.0 mass % (in reference to the total amount of the lubricating oil composition). Moreover, while there is no particular limitation on the inclusion proportion for the phenol-based oxidation inhibitor, it should be, for example, between 0.1 and 2.0 mass % (in reference to the total amount of the lubricating oil composition).

The lubricating oil composition according to the present invention may include a sulfur-including additive. Note that the sulfur-including additive indicated here indicates a sulfur compound other than the ZnDTP and MoDTC described above, and may be selected as a component that is further added after adding the MoDTC.

That which is known may be used for this sulfur-including additive, which may be, for example, hydrogen sulfide, a sulfur cross-linked metal phenate, dihydrocarbyl polysulfide, a dithiocarbamate other than MoDTC, or the like.

Note that while there is no particular limitation on the inclusion proportion for the sulfur-including additive, it should be between 0.1 mass % and 2.0 mass %, in relation to the lubricating oil composition as a whole.

As required, additives other than the above, such as oxidation inhibitors, ashless dispersing agents, metal cleaning agents, friction adjusting agents, rust inhibiting agents, anti-forming agents, or the like, may also be added to the lubricating oil composition according to the present invention. Moreover, an additive package, wherein some or all of the additives to be mixed in are packaged, may be used (or may be used as well).

Note that while there is no particular limitation on the inclusion proportion of the other components such as this, it should be between 10 mass % and 30 mass %, relative to the lubricating oil composition as a whole, as additives other than the base oil, taking into consideration also dilution of the oil in which the various additives, including the viscosity index improving agent, are included.

While there is no particular limitation on the method for manufacturing the lubricating oil composition according to the present invention, the manufacturing may be through, for example, adding and mixing the various components described above through an arbitrary process.

The lubricating oil composition according to the present invention is provided with all of the following characteristics (A) through (E):

(A) high temperature high shear viscosity (HTHSV (ASTM D4683 or ASTM D5481)) at 150° C., 106 s-1 is 1.0 mPa·s or more; (B) kinetic viscosity (KV (JIS K2283)) at 100° C. is 3.0 mm2/s or more; (C) HTHSV50° C./HTHSV150° C. is 6.50 or less; (D) KV50° C./HTHSV150° C. is 8.00 or less; and (E) NOACK evaporation amount (JPI-5S-41) is 15 mass % or less.

In the lubricating oil composition according to the present invention, having the HTHSV 50° C./HTHSV 150° C. be no greater that 6.50 and the KV 50° C./HTHSV 150° C. be no greater than 8.00 enables an improvement in fuel economy and satisfaction of a NOACK evaporation (JPI-5S-41) of no greater than 15 mass %, even given conditions of (A) 150° C., 106 s-1 high-temperature/high-shear viscosity (HTHSV (ASTM D4683 or ASTM D5481)) no less than 1.0 mPa·s and a 100° C. kinematic viscosity (KV) no less than 3.0 mm²/s.

Note that specifically, in order to achieve (C) and (D), above, it is effective to reduce the solubility, relative to the base oil, below that of existing viscosity index improving agents, and to increase the temperature of complete dissolution of the polymer. For example, if the viscosity index improving agent is PMA, it is possible to make adjustments through increasing the polarity of the PMA by increasing the chain length of the R (long alkyl chain) of the —COOR group that is a structural element of the PMA.

The lubricating oil composition according to the present invention can be used as a lubricating oil composition for an ordinary internal combustion engine, but is particularly well-suited as a lubricating oil composition for a PHV internal combustion engine and/or for an internal combustion engine for an idling-stopping vehicle.

Examples

Lubricating oil compositions according to the invention and Reference Examples 1 through 5 were prepared through mixing the raw materials listed below so as to have the blending quantities (mass %) shown in Table 1. Note that in the present invention, a composition wherein the 150° C. HTHSV is no greater that 2.5 is classified corresponding to 0W-20, and if less than this, is classified corresponding to 0W-16.

Base Oils

-   -   Shell XHVI (registered trademark) 4 (GTL base oil);     -   Shell XHVI (registered trademark) 3 (GTL base oil).

DI Package

The primary ingredients in the package used are shown below.

-   -   Package A.

A mixture of a highly refined mineral oil, a succinimide-based ashless dispersing agent, a calcium-based metal cleaning agent, ZnDTP, and an amine-based oxidation inhibitor.

-   -   Package B.

A mixture of a highly refined mineral oil, a succinimide-based ashless dispersing agent, a calcium-based metal cleaning agent, a magnesium-based metal cleaning agent, ZnDTP, and an amine-based oxidation inhibitor.

-   -   Package C.

A mixture of a highly refined mineral oil, a succinimide-based ashless dispersing agent, a magnesium-based metal cleaning agent, a calcium-based metal cleaning agent, ZnDTP, an amine-based friction adjusting agent, an amine-based oxidation inhibitor, and a phenol-based anti-oxidizing agent.

Viscosity Index Improving Agent

-   -   Viscosity index improving agent E: Non-comb PMA;     -   Viscosity index improving agent F: OCP;     -   Viscosity index improving agent D, G, and H: Comb PMAs.

Here the viscosity index improving agents D, G, and H are comb PMAs manufactured under different conditions, to have differences in numbers of repetitions, chain lengths of the long alkyl chains, and the like, to exhibit mutually differing polarities.

Friction Adjusting Agent

-   -   Sakuralube 525 (MoDTC (molybdenum dithiocarbamate), manufactured         by ADEKA Co.).

Anti-Foaming Agent

-   -   A 3 mass % solution wherein polymethyl siloxane (silicone oil)         with a weight average molecular weight of approximately 30,000         is dissolved, at DCF 3 mass %, into JIS No. 1 kerosene.

Here the concentrations of Ca, Mg, Mo, P, Zn, N, and S (mass %, in reference to the total amount of the lubricating oil composition) in Reference Examples 1 through 5 and Examples 1 through 4 are shown in Table 2. The measurement methods are based on JPI-5S-38 for B, Ca, Mg, Mo, P, and Zn, based on JIS K2609 for N, and based on JIS K2541-4 (the radiostimulation method) for S.

Evaluation

Next, for each of the individual lubricating oil compositions, the high-temperature/high-shear viscosities (50° C. and 150° C.) were measured based on ASTM D5481, the kinematic viscosities (40° C., 50° C., and 100° C.) were measured based on JIS K2283, and the NOACK evaporation was measured based on JPI-5S-41, and the reduction in fuel consumption was also evaluated. The evaluation results are shown in Table 3. The method for evaluating the fuel economy (the reduction in fuel consumption) was as follows.

An engine was driven by an electric motor, and the force required to do so (the friction torque) was measured by a torque meter. A four-cylinder in-line 2.0-L direct injection engine was used for the engine, with a test oil temperature of 50° C., and a rotational speed of 2,000 RPM (where the lubricating oil composition of Reference Example 1 was used as a reference oil).

Note that 50° C. was selected as the test oil temperature, envisioning the state wherein a typical passenger vehicle has just been started, or traveling conditions wherein the engine oil temperature does not increase substantially, in an idle stopping vehicle or a PHV.

In Table 3 it can be appreciated that, when compared to the corresponding lubricants of the same viscosity grades, that is, when for Reference Example 1, Example 1, and Example 3, which correspond to 0W-20, are compared, and Reference Example 2, Reference Example 3, Example 2, and Example 4, which correspond to 0W-16, are compared, the fuel economy can be improved through having the HTHSV 50° C./HTHSV 150° C. be no greater than 6.50, and the KV 50° C./HTHSV 150° C. be no greater than 8.00.

TABLE 1 Reference Example 1 (Reference Reference Reference Reference Reference Oil) Example 2 Example 3 Example 4 Example 5 Corresponding Corresponding Corresponding Corresponding Corresponding to 0 W-20 to 0 W-16 to 0 W-16 to 0 W-16 to 0 W-16 SHELL XHVI 82.82 74.67 74.07 77.07 75.57 4 SHELL XHVI 8.50 8.50 8.50 8.50 3 Package A 9.05 Package B 9.30 9.30 9.30 9.30 Package C Sakuralube 1.00 1.00 1.00 1.00 1.00 525 (MoDTC) Viscosity 4.70 6.50 Index Improving Agent D Viscosity 2.40 4.10 Index Improving Agent E Viscosity 5.60 Index Improving Agent F Viscosity 7.10 Index Improving Agent G Viscosity Index Improving Agent H DCF 003 0.03 0.03 0.03 0.03 solution Total 100.00 100.00 100.00 100.00 100.00 Example 1 Example 2 Example 3 Example 4 Corresponding Corresponding Corresponding Corresponding to 0 W-20 to 0 W-16 to 0 W-20 to 0 W-16 SHELL XHVI 73.37 73.87 72.65 76.27 4 SHELL XHVI 6.50 8.50 6.50 6.00 3 Package A Package B 9.30 9.30 Package C 10.2 10.2 Sakuralube 100 1.00 1.00 1.00 525 (MoDTC) Viscosity Index Improving Agent D Viscosity Index Improving Agent E Viscosity Index Improving Agent F Viscosity Index Improving Agent G Viscosity 9.80 7.30 9.62 6.50 Index Improving Agent H DCF 0.03 0.03 0.03 0.03 solution Total 100.00 100.00 100.00 100.00

TABLE 2 Reference Example 1 (Reference Reference Reference Reference Reference Oil) Example 2 Example 3 Example 4 Example 5 Corresponding Corresponding Corresponding Corresponding Corresponding to 0 W-20 to 0 W-16 to 0 W-16 to 0 W-16 to 0 W-16 B 0.01 <0.01 <001 <0.01 <0.01  Ca 0.22 0.15 0.15 0.15 0.15 Mg — 0.06 0.06 0.06 0.06 Mo 0.10 0.10 0.10 0.10 0.10 P 007 0.07 0.07 0.07 0.07 Zn 0.09 0.08 0.08 0.08 008    N 0.10 0.09 0.09 0.09 0.09 S 0.34 0.36 0.36 0.36 0 36 Example 1 Example 2 Example 3 Example 4 Corresponding Corresponding Corresponding Corresponding to 0 W-20 to 0 W-16 to 0 W-20 to 0 W-16 B <0.01 <0.01 0.01 0.01 Ca 0.15 0.15 0.14 0.14 Mg 0.06 0.06 0.05 0.05 Mo 0.10 0.10 0.10 0.10 P 0.07 0.07 0.07 0.07 Zn 008 0.08 0.08 0.08 N 0.09 0.09 0.09 0.09 S 0.36 0.36 0.38 0.38

TABLE 3 Reference Example 1 Reference Reference Reference Reference Reference Oil) Example 2 Example 3 Example 4 Example 5 Corresponding Corresponding Corresponding Corresponding Corresponding to 0 W-20 to 0 W-16 to 0 W-16 to 0 W-16 to 0 W-16 KV 50° C. (mm2/s) 23.1 18.2 17.9  23 4 24.8  HTHSV 50° C. (TBS) 16.1 14.4 14.2  15.2 16.6  (mPa − s) HTHSV 150° C. (TBS) 2.55 2.24 2.19  2.29 2.29 (mPa · s) KV 40aC (mm2/s) 23.1 25.2 24.8  32.4 35.1  KV 100° C. (mm2/s) 7.75 6.40 6.13  7.33 7.08 NOACK 250° C. (%) 15 15 15    15   15    HTHSV 50° C./HTHSV 6.33 6.41 6 49  6.65 7 23 150° C. (—) KV 50° C./HTHSV 9.05 8.13 8.18  10.21 10.82  150° C. (—) 2,000 RPM Torque 0.0 1.6 2.2  — — Improvement Ratio (%) Example 1 Example 2 Example 3 Example 4 Corresponding Corresponding Corresponding Corresponding to 0 W-20 to 0 W-16 to 0 W-20 to 0 W-16 KV 50° C. (mm2/s) 19.0 17.9 19.0 17.9 HTHSV 50° C.(TBS) 14.8 14.2 15.1 14.5 (mPa − s) HTHSV 2.52 2.26 2.55 2.25 150° C. (TBS) mPa · s) KV 40aC (mm2/s) 26.1 24.7 26.2 24.8 KV 100° C. 6.90 6.17 6.86 6.07 (mm2/s) NOACK 250° C. (%) 15 15 15 15 HTHSV 5.85 6.28 5.91 6.44 50° C./HTHSV 150° C. (—) KV 50° C./HTHSV 7.54 7.93 7.44 7.95 150° C. (—) 2,000 RPM 2.8 3.5 1.8 2.8 Torque Improvement Ratio (%) 

1. A lubricating oil composition for an internal combustion engine, comprising a GTL (Gas To Liquid) base oil synthesized by the Fischer-Tropsch method and a viscosity index improver, wherein the content of the viscosity index improver relative to the total amount of lubricating oil composition is 0.1 to 20 mass % by resin amount, and the lubricating oil composition satisfies the following (a) to (e): (a) high temperature high shear viscosity (HTHSV (ASTM D4683 or ASTM D5481)) at 150° C., 106 s-1 is 1.0 mPa·s or more; (b) kinematic viscosity (KV (JIS K2283)) at 100° C. is 3.0 mm2/s or more; (c) HTHSV50° C./HTHSV 150° C. is 6.50 or less; (d) KV50° C./HTHSV150° C. is 8.00 or less; and (e) NOACK evaporation amount (JPI-5S-41) is 15 mass % or less.
 2. The lubricating oil composition of claim 1, comprising one or more base oils having KV100° C. of 1 to 8 mm2/s, a viscosity index of 110 or more, % CA by ASTM D3238 of 5 or less, and % CP by ASTM D3238 of 60 or more, wherein: the content of the base oils relative to the total amount of the lubricating oil composition is 50 mass % or less, and a fraction of an entire base oil at 380° C. or less in gas chromatography distillation by ASTM D2887 is 10 mass % or less.
 3. The lubricating oil composition of claim 1, wherein at least one of (f) through (i), below, is satisfied: (f) the lubricating oil composition includes a metal-including detergent having at least one selection from Ca and Mg, and [Ca]+[Mg]=0.10 to 0.25, where [Ca], [Mg] are respectively concentrations (mass %) of calcium and magnesium in the lubricating oil composition; (g) the lubricating oil composition contains a succinimide ashless dispersant and/or a boron modified succinimide ashless dispersant, and the dispersants are 0.01 to 0.20 mass % (based on a total amount of the lubricating oil composition) in terms of nitrogen concentration; (h) the lubricating oil composition includes ZnDTP of 0.03 to 0.09 mass % (based on the total amount of the lubricating oil composition) in terms of phosphorus concentration; and/or (i) the lubricating oil composition includes an organic molybdenum compound of 0.01 to 0.12 mass % (based on the total amount of the lubricating oil composition) in terms of Mo concentration.
 4. The lubricating oil composition of claim 1, including at least one selection from a corrosion inhibitor, a phenol-based antioxidant, an amine-based antioxidant, and a sulfur-containing additive.
 5. The lubricating oil composition of claim 1, wherein the viscosity index improver is a comb polymer, preferably wherein the comb polymer comprises (1) repeating units derived from polyolefin-based macro monomers, and (2) repeating units derived from low-molecular-weight monomers selected from a group comprising styrene monomers having between 8 and 17 carbon atoms, alkyl(meth)acrylates having between 1 and 10 carbon atoms in an alcohol base, vinyl esters having between 1 and 11 carbon atoms in an acyl, vinyl ethers having between 1 and 10 carbon atoms in an alcohol base, (di)alkyl fumarate having between 1 and 10 carbon atoms in an alcohol base, (di)alkyl maleates having between 1 and 10 carbon atoms in an alcohol base, and mixtures of these monomers, included in the main chain. 